All they needed to do was talk tbh
Talk what? They didn't know why kouta couldn't sense his pheromones anymore so just talking wouldn't have helped much.
If they communicated better at the start, they might have decided to go ahead with the bonding before it got this bad.
And if they talked about it properly when the issue came up I'm sure he would've been dragged to the hospital much sooner. Since they both one-sidedly assumed a reason, talking would've ruled those out is all I'm saying. Realising he should go to the hospital was the real problem.
You're right in that it should've been a no-brainer tho
See? All they needed to do was go to the doctors. I've been screaming at them to visit a doctor at the first sign of this 'not sensing pheromones' problem but..sigh der aaye durust aaye. Live happily you idiots.┗ ( T﹏T )┛